Lock the two things you want to keep fixed. The unlocked one will adjust automatically. Most common: lock Number of photos and Total length to get Time per photo.
Choose your inputs
We’ll round down if needed.
seconds
Common choices: 3–6 seconds.
Total slideshow length
Tip: Lock any two fields. Adjust the third by typing in the unlocked field’s siblings.
Optional timing
seconds/photo
Add for cross-fades or motion.
seconds total
Opening title, closing slide, etc.
Enter values and use the locks. I’ll keep everything in sync.